Integrated circuits, in particular those provided with memories containing sensitive information, must be, as much as possible, protected against attacks, in particular those intended to uncover stored data.
A possible attack can be carried out via the rear face of an integrated circuit, using a laser beam.
The effectiveness of such an attack increases when the substrate of the integrated circuit is thinned by the attacker from the rear face thereof such as to get as close as possible to the components of the integrated circuit, which are produced at the front face thereof. The thinning of the rear face of the integrated circuit can occur, for example, using a focused ion beam (FIB) and/or using a polishing/abrasion step.
Means exist which make it possible to detect a thinning of the substrate via the rear face thereof. However, these means sometimes have a low level of integration, and sometimes can disrupt the operation of the components located close by.
These existing means can, for example, use a resistance that varies with the thinning of the substrate. However, this type of solution can be a source of errors, particularly for integrated circuits having a variable temperature, which varies the value of the resistance even when there is no thinning.
Furthermore, it is possible for the existing devices to be modified by an attacker prior to the detection, such as to falsify the result thereof, for example by forcing an output signal to a state indicating an absence of detection.
Thus, according to an embodiment, a method and a device are proposed which make it possible to reliably detect a thinning of the substrate via the rear face thereof, the device having a reduced spatial requirement.